Salted Coffee Custard Pie

Name: Salted Coffee Custard Pie
Ingredients: 6 Tbsp. unsalted butter, melted, slightly cooled, plus more, room temperature, for pan; 2 cups (180 g) old-fashioned oats; ¼ cup (31 g) all-purpose flour; ¼ cup (packed; 50 g) dark brown sugar; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt; 1 cup (packed; 200 g) dark brown sugar; 2 Tbsp. all-purpose flour; 2 Tbsp. instant espresso powder, plus more for serving (optional); 2 tsp. Diamond Crystal or 1 tsp. Morton kosher salt, divided; 3 large eggs; ½ cup (1 stick) unsalted butter, melted, slightly cooled; 1 Tbsp. plus 1 tsp. vanilla bean paste or vanilla extract; 1 cup cold-brew coffee concentrate (preferably Grady’s); 2⅔ cups heavy cream, divided; ½ cup mascarpone; 4 Tbsp. granulated sugar; Flaky sea salt; A 9-diameter deep pie dish